As a light emitting diode (LED), particularly as a blue or UV LED having an emission wavelength of approximately 250 nm to 550 nm, a high-brightness LED product using a compound semiconductor made of a GaN compound such as GaN, GaAlN, InGaN or InAlGaN has been obtained. Also, a high-definition full color image may be formed using a technique of combining red and green LED's with a blue LED. For example, a technique of preparing a white LED by combining a blue LED or UV LED with a phosphor has been known. Such LED's have been increasingly required for backlighting or general lighting in liquid crystal displays (LCD's).
As an LED encapsulant, an epoxy resin having high adhesive strength and excellent dynamic durability has been widely used. However, the epoxy resin has problems in that it has low transmittance with respect to light having blue to UV wavelength regions, and also shows poor lightfastness. Therefore, techniques in order to solve the problems as described above have been proposed, for example, in Japanese Patent Laid-Open Publication Nos. Hei11-274571, 2001-196151 and 2002-226551. However, the encapsulants described in these literatures show insufficient lightfastness.
As a material that has excellent lightfastness with respect to the low wavelength range, a silicone resin has been known. However, the silicone resin has disadvantages in that its heat resistance is poor, and its surface becomes sticky after curing. Also, in order to effectively apply the silicone resin as an LED encapsulant, characteristics such as a high refractive property, crack resistance, surface hardness, adhesive strength and thermal shock resistance must be secured.